Positional encoder and control rod position indicator for nuclear reactor using same

ABSTRACT

A cam is immersed in water at an elevated temperature and/or pressure. A reciprocating cam follower also immersed in the water contacts a surface of the cam. The cam follower includes a permanent magnet. An electrically conductive coil is magnetically coupled with the permanent magnet such that movement of the cam follower induces an electrical signal in the electrically conductive coil. A sealed housing also immersed in the water contains the electrically conductive coil and seals it from contact with the water. Leads of the coil are electrically accessible from outside the sealed housing and from outside the water. Alternatively, the cam includes magnetic inserts, the cam follower is replaced by a sensor arm of magnetic material, and the sensor arm and/or the inserts are magnetized whereby rotation of the rotary element causes time modulation of the magnetic coupling and induces coil voltage.

This application claims the benefit of U.S. Provisional Application No.61/625,135 filed Apr. 17, 2012. U.S. Provisional Application No.61/625,135 filed Apr. 17, 2012 is hereby incorporated by reference inits entirety.

BACKGROUND

The following relates to the positional encoder arts, nuclear reactorarts, nuclear reactor operating arts, and related arts.

Pressure vessels advantageously enable the creation of high pressureenvironments, which are optionally also at high temperature. Forexample, nuclear reactors of the pressurized water reactor (PWR) varietyemploy a pressure vessel to maintain primary coolant water in asub-cooled state that suppresses void (i.e. bubble) formation andincreases efficiency of the primary coolant in performing neutronmoderator and thermal transport operations. In one contemplated PWRdesign, the subcooled primary coolant water is expected to be maintainedat a pressure above 16.0 MPa and a temperature above 550° F., with somedifferences between the hot and cold legs of the primary coolant flowcircuit. This is merely an illustrative example, and the designoperating temperatures and pressures depend upon the specific reactordesign. Other useful applications of pressure vessels include steamdrums, various material processing systems that subject material to hightemperature and/or pressure, chemical processing systems, and so forth.

Producing motion inside a pressure vessel is a challenging task, due tothe high pressure, optional high temperature, and other factors. Oneapproach is external magnetic coupling through the pressure vessel wall,but this approach has practical access limitations. Another approach isto use a bellows, but this also has access limitations, and moreover thelong-term mechanical stress on the bellows can lead to componentfailure. Another approach is to employ a glandless or glanded mechanicalvessel penetration, but this has similar problems.

A more flexible approach to providing motion inside a pressure vessel isto employ a canned internal motor that is disposed inside the pressurevessel. For example, the mPower™ reactor design is contemplated toinclude canned motors disposed inside the reactor pressure vessel foroperating the control rod drive mechanisms (CRDMs), and other reactordesigns contemplate employing internal reactor coolant pumps (RCPs) withcanned motors. These approaches tend to require higher levels ofengineering expertise and design since the materials of the motor mustbe capable of withstanding the high temperature and pressure inside thepressure vessel, and any components immersed in the primary coolantwater should also be robust against long-term exposure.

A related problem is to perform measurement of mechanical motion at hightemperature and/or pressure. This problem arises in both testing andoperational phases of the deployment of a pressure vessel-based system.For example, validation of the mPower™ reactor design is expected toinclude testing of CRDM units at operational temperature and pressure ina test facility prior to deployment in an operational reactor. Whileoperation of the CRDM may be inferred from measuring electrical inputand response of the operating CRDM motor, and from post-testinginspection of the CRDM unit, it would be desirable for the testing toinclude direct measurement of the motion generated by the CRDM in thepressure vessel at operational temperature and pressure.

Performing motion measurement in a high pressure and/or high temperatureenvironment faces similar problems to those faced in producing motion insuch environments. Additionally, cost is a more significant issue,especially for sensors used in testing. It is not desirable for testsensors to be expensive components, since they are not operationalelements of the nuclear reactor. However, the test sensors should berobust and reliable in order to produce valid test data.

SUMMARY

In one embodiment, a sensor comprises: an electrically conductive coil;a housing having an unsealed inner volume, the electrically conductivecoil being sealed inside the housing and encircling the unsealed innervolume; and a movable element including (i) a permanent magnet that isdisposed in the unsealed inner volume and is magnetically coupled withthe electrically conductive coil and (ii) a contact portion extendingoutside the housing, the movable element being movable respective to thehousing such that force applied to the contact portion moves thepermanent magnet respective to the electrically conductive coil togenerate an electrical signal in the electrically conductive coil. Thesensor may be a passive sensor that does not receive electrical powerand has only two electrical leads.

In accordance with another aspect, an apparatus includes a sensor as setforth in the immediately preceding paragraph, and a rotary cam, and themovable element of the sensor comprises a cam follower engaging a sidesurface of the rotary cam that is shaped to produce reciprocation of thecam follower when the rotary cam rotates. The apparatus may furtherinclude a readout device connected to measure the electrical signalgenerated in the electrically conductive coil, an electronic dataprocessing device configured to compute a rotation rate or rotationdistance of the rotary cam based on the measured electrical signal. Therotary cam may be a nut of a control rod drive mechanism (CRDM) thatengages a screw of the CRDM, and the electronic data processing devicemay be further configured to compute a linear translation rate or lineartranslation distance of the screw based on the computed rotation rate orrotation distance and a thread pitch of the screw. In accordance withanother aspect, an apparatus includes a sensor as set forth in theimmediately preceding paragraph, and a control rod drive mechanism(CRDM) including a screw or a rack, wherein the movable element of thesensor comprises a cam follower engaging the screw or rack such thatthreads of the screw or gear teeth of the rack produce reciprocation ofthe cam follower as the cam moves linearly.

In accordance with another aspect, an apparatus comprises: a camimmersed in water at a temperature of at least 212° F.; a reciprocatingcam follower contacting a surface of the cam, the reciprocating camfollower also immersed in the water, the reciprocating cam followerincluding a permanent magnet; an electrically conductive coilmagnetically coupled with the permanent magnet of the reciprocating camfollower such that movement of the cam follower induces an electricalsignal in the electrically conductive coil; and a sealed housingimmersed in the water and containing the electrically conductive coil,the sealed housing sealing the electrically conductive coil from contactwith the water, leads of the electrically conductive coil beingelectrically accessible from outside the sealed housing and from outsidethe water. The sealed housing may have an unsealed inner cavity in whichthe cam follower is mounted, the permanent magnet of the cam followerbeing disposed inside the cavity, the cam follower including a contactportion extending out of the cavity and contacting a surface of the cam.

In accordance with another aspect, an apparatus comprises: a rotaryelement made of a non-magnetic material with a side surface having oneor more inserts made of a magnetic material; a sensor arm made of amagnetic material, the sensor arm contacting the side surface of therotary element; an electrically conductive coil magnetically coupledwith the sensor arm wherein at least one of (i) the sensor arm and (ii)the inserts of the rotary element are magnetized such that rotation ofthe rotary element causes time modulation of the magnetic couplingbetween the electrically conductive coil and the sensor arm so as toinduce a voltage in the electrically conductive coil; and a sealedhousing containing the electrically conductive coil, leads of theelectrically conductive coil being electrically accessible from outsidethe sealed housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various process operations and arrangements ofprocess operations. The drawings are only for purposes of illustratingpreferred embodiments and are not to be construed as limiting theinvention.

FIG. 1 diagrammatically shows a sensor system operating to encode speedor position of a rotary cam.

FIG. 2 diagrammatically shows a plan view of the sensor engaging the camwherein the cam includes an asymmetric set of two features.

FIG. 3 diagrammatically shows an electrical signal produced by thesensor operating as shown in FIG. 2, wherein the electrical signalincludes a signal feature (top plot) or a distinguishable time-reversedsignal feature (bottom plot) in the measured electrical signal dependingupon rotation direction of the rotary cam.

FIGS. 4 and 5 diagrammatically show side sectional and perspectiveviews, respectively, of an embodiment of the sensor of FIG. 1.

FIGS. 6 and 7 show perspective and end views, respectively, of a camsuitably employed in the sensor system of FIGS. 1 and 2.

FIGS. 8 and 9 show perspective and end views, respectively, of anothercam suitably employed in the sensor system of FIGS. 1 and 2.

FIGS. 10 and 11 show perspective and end views, respectively, of anotherrotary element suitably employed in the sensor system of FIGS. 1 and 2,which employs magnetic modulation rather than mechanical reciprocation.

FIGS. 12 and 13 show perspective and end views, respectively, of anothercam suitably employed in the sensor system of FIGS. 1 and 2.

FIG. 14 diagrammatically shows a nuclear reactor of the integralpressurized water reactor (integral PWR) variety diagrammaticallyindicating placement of the sensor of FIG. 1 for measuring positionand/or translation speed of the control rod assembly produced by acontrol rod drive mechanism (CRDM).

FIG. 15 diagrammatically shows mechanical components of a control roddrive mechanism (CRDM) including a nut engaging a screw, and furtherdiagrammatically shows two suitable placements of the sensor of FIGS. 1and 2 for measuring position and/or translation speed of the control rodassembly produced by the CRDM, one placement engaging the nut and theother engaging the screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosed herein are sensors for measuring motion in high temperatureand/or high pressure environments. The sensors are described withparticular reference to the application of testing and/or monitoring aninternal control rod drive mechanism (CRDM) of a nuclear reactor, suchas the contemplated Babcock & Wilcox mPower™ PWR design. However, thedisclosed sensors can be constructed at low cost and with highreliability, and are expected to find use in substantially any motionmeasurement application performed inside a pressure vessel at highpressure (and, optionally, high temperature). The disclosed sensors arealso expected to find use in other environments, such as monitoringmotion in a boiling water environment at atmospheric pressure (e.g.,water in a liquid or mixed liquid/steam phase at or above 212° F.). Thedisclosed sensors employ a combination of a sealed electricallyconductive coil magnetically coupled with an unsealed cam follower thatengages a surface of the object (i.e., a cam) that is undergoing motionmeasurement. This design advantageously seals the sensitive coilcomponent, but does not seal the cam follower.

The disclosed sensors can be constructed as passive components employinga cam follower with a permanent magnet that magnetically couples the camfollower with the sealed electrically conductive coil. As a passivecomponent, the sensor does not require any operating power andaccordingly requires only two signal leads to pass through the pressurevessel. This minimal electrical wiring is advantageous in an environmentsuch as a nuclear reactor in which a significant portion of theelectrical cabling is mineral insulated (MI) cabling having a relativelylarge minimum bend radius that makes cable routing inside the reactor acomplex endeavor.

With reference to FIG. 1, a sensor 10 includes an electricallyconductive coil 12 sealed in a housing 14, and a movable element 16including a permanent magnet 18 and a contact portion 20. The housing 14includes a sealed outer volume 22 containing the electrically conductivecoil 12, and a cavity or unsealed inner volume 24 in which the movableelement 16 is mounted with the magnet 18 disposed inside cavity 24. Inthe illustrative sensor 10, the unsealed inner volume 24 is defined inpart by a wall 26 having an opening 28 out of which the contact portion20 of the movable element 16 extends, and a spring 30 biases a stop 32of the movable element 16 against the wall 26.

The movable element 16 of the sensor 10 is a reciprocating cam follower16 whose contact portion 20 contacts a surface of a cam 40. The surfaceof the cam 40 that is contacted by the cam follower 16 is a cam surface42, and is contoured so that as the cam surface 42 moves respective tothe cam follower 16 it causes the cam follower 16 to reciprocate, i.e.to move linearly back-and-forth. The illustrative cam 40 is a rotary camthat is shown only in part in FIG. 1; the rotary cam 40 rotates about arotational axis 44. In operation, the compressed spring 30 pushes thecontact portion 20 of the cam follower 16 against the cam surface 42,and as the cam 40 rotates the cam surface 42 passes over the contactportion 20 and, when the surface contour transitions to higher relief,it pushes the cam follower 16 further into the unsealed cavity 24against the force of the compressed spring 30. When the surface contourpressing against the contact portion 20 transitions to lower relief asthe cam 40 rotates, the spring 30 returns the cam follower 16 to itsrest position in which the stop 32 is pressed against the wall 26 of thecavity 24. (Note: depending upon the lowest relief of the cam surface 42and the position of the sensor 10 respective to the cam 40, in someembodiments the cam follower 16 may never return completely to the restposition. That is, in some embodiments the cam surface 42 presses thecam follower 16 some distance into the cavity 24 even at the lowestrelief point of the cam surface 42). As the rotary cam 40 rotates overmultiple revolutions, the cam follower 16 thus follows the cam surface42 between its lowest and highest relief points, thus producing areciprocating (i.e. back-and-forth) motion of the cam follower 16responsive to rotation of the cam 40. The reciprocating movement of thecam follower 16 includes reciprocating movement of the permanent magnet18 which is part of the cam follower 16. Reciprocation of the permanentmagnet 18 produces a time-varying magnetic field inside the coil 12which encircles the magnet 18. In accord with Maxwell's equations, thistime-varying magnetic field generates a time-varying voltage in theelectrically conductive coil 12 (and a time-varying electric current inthe coil 12 if it is connected with an electrically conductiveelectrical circuit).

The sensor 10 and the cam 40 are disposed in a pressure vessel 50(diagrammatically indicated by a containing polygon in FIG. 1)containing an ambient, e.g. water, held at a certain temperature andpressure by the pressure vessel 50 and ancillary components (not shown).The sensor 10 and cam 40 are immersed in the water (or other ambient);however, because the electrically conductive coil 12 is sealed insidethe housing 14 (e.g., is located inside the sealed volume 22), theelectrically conductive coil 12 is not exposed to the water (or otherambient).

The cam follower 16 includes the magnet 18. In a suitable embodiment,the cam follower 16 is a rod having one end protruding out the opening28 of the cavity 24 to form the contact portion 20, and the opposite enddisposed inside the cavity 24 and encircled by the electricallyconductive coil 12. The magnet 18 is preferably a permanent magnet, bywhich it is meant that the magnet 18 has sufficient permanentmagnetization to generate an effective voltage in the electricallyconductive coil 12. In some embodiments the cam follower 16 includes aferromagnetic main body and the permanent magnet 18 is separate from theferromagnetic main body and is magnetically connected to theferromagnetic main body. Alternatively, the entire cam follower 16 canbe a single piece (e.g. a single machined or cast ferromagnetic element)that is magnetized, so that the entire cam follower forms the magnet(embodiment not shown). The cavity 24 is an unsealed cavity, so thecavity 24 is filled with the ambient (e.g., water) contained in thepressure vessel 50. This means that the cam follower 16 including themagnet 18, as well as the spring 30, are exposed to the water (or otherambient). However, these components can be made of material such assteel that is robust against high temperatures and pressures. The magnet18 is made of any suitably robust material that can be permanentlymagnetized with sufficient magnetization. In some embodiments, themagnet 18 is a samarium cobalt (SmCo) magnet; however, other magneticmaterials are also contemplated.

With continuing reference to FIG. 1, electrical leads of theelectrically conductive coil 12 of the sensor 10 are electricallyaccessible from outside the pressure vessel 50. For example, in theillustrative embodiment the leads are connected with a (diagrammaticallyindicated) mineral-insulated cable (i.e., MI cable) 52 that passesthrough (or electrically connects to) a vessel penetration passingthrough the wall of the pressure vessel 50. This approach is suitable,for example, in a nuclear reactor where MI cabling is commonly used forelectrical interconnects inside the reactor. Advantageously, the sensor10 is a passive device and includes only two signal leads (connecting tothe electrically conductive coil 12) and no power leads.

To provide movement measurement, the output of the sensor 10 connectswith an electronic data processing device 60, such as a computer,microcontroller or microprocessor with suitable ancillary electronics(memory, et cetera), or so forth to implement data processing to convertthe electrical signal of the coil 12 to a movement measure. Inillustrative FIG. 1, the electronic data processing device 60 includes(or is connected with) a readout device 62 that generates a digitizedrepresentation of the electrical signal induced in the coil 12 byreciprocation of the magnet 18 responsive to movement of the cam surface42. The readout device 62 may, for example, be a standalone voltagemeter with a digital output, or may be an analog to digital converter(ADC) card installed in a computer embodying the electronic dataprocessing device 60. The output of the readout device 62 is a digitalrepresentation of the voltage-versus-time signal read from the coil 12,for example as a time sequence of digitized voltage samples acquiredfrom the coil 12 by the readout device 62.

The processing of the readout voltage versus time signal depends uponthe nature of the mechanical motion being measured. For example, if therotary cam 40 is expected to be at a constant rotation speed, then thecontouring of the cam surface 42 is expected to produce avoltage-versus-time signal with a frequency component equal to therotation frequency (or to a multiple thereof). For example, if the camsurface 42 is a side surface of the rotary cam 40 of constant radiusexcept for a single feature (e.g., a bump or depression) located at asingle discrete point along the circumference of the side surface, thenthe voltage versus time signal should have a single pulse per revolutionof the cam 40, due to movement of the magnet 18 caused by the camfollower 16 passing over the feature. Thus, a frequency detector 70,such as a fast Fourier transform (FFT) processor, suitably detects thefrequency of the pulses which equals the rotation speed of the cam 40.If the cam 40 is a nut driving a screw, as in the case of a control roddrive mechanism (CRDM) of a nuclear reactor employing a nut/screwmechanism, then this frequency is a CRDM motor rotational frequency 72.(This assumes that the cam 40 is a nut forming the rotor of a CRDMmotor). If the screw pitch 74 of the screw is known, then a linearvelocity calculator 76 can compute the linear velocity 78 of the screw(which is assumed here to carry the control rod assembly) as rotationspeed times thread pitch. Note that this approach can track changes inthe rotational speed of the cam 40 so long as those changes are on along enough time scale for the FFT or other frequency detector 70 totrack the changes in rotational frequency. Also, the one-to-one ratiobetween electrical frequency and mechanical rotation speed may notnecessarily hold: For example, if the cam surface 42 includes twofeatures spaced 180° apart along the circumference of the side wall ofthe rotary cam 40, then two pulses per revolution will be observed inthe voltage-versus-time signal (one for each feature), and so theelectrical frequency will be twice the mechanical rotation frequency.This can be readily accounted for in the data processing based on theknown contour of the cam surface 42.

If the cam 40 is not expected to rotate at a constant rate, the sensor10 can still be used to track rotational motion and (in the case of anut/screw assembly) linear motion of a driven screw. In this approach, apulse counter 80 counts the pulses in the voltage versus time signal. Ifthe cam surface 42 includes a single feature (bump or depression), theneach pulse corresponds to a single revolution of the cam 40, and so adistance integrator 82 can compute the screw translation distance sinceeach counted pulse corresponds to a linear translation equal to thethread pitch 74. If the initial position of the screw is known, thenthis integrated distance yields a linear position 84 for the screw.

With reference to FIGS. 2 and 3, if the cam surface contouring issuitably constructed then the sensor 10 can additionally oralternatively be used to determine rotation direction of the rotary cam40. FIG. 2 shows a plan view (i.e., top or bottom view) of the cam 40with its cam surface 42, which in this example includes a first featureF1 (a bump, in this case, although a depression could alternatively beemployed) and a second feature F2 that is different from the firstfeature F1. In the illustrative example, feature F1 is a larger bumpthan feature F2. Moreover, there is asymmetry in the spacing of featuresF1, F2 around the circumference of the cam surface 42, in that the twofeatures F1, F2 are not spaced apart by 180°. FIG. 2 alsodiagrammatically shows the sensor 10 including the housing 14 and thecontact portion 20 of the cam follower protruding from the housing 14 tocontact the cam surface 42. FIG. 2 also indicates clockwise (CW) andcounterclockwise (CCW) rotation directions. FIG. 3 plots pulses in thevoltage versus time signal for clockwise rotation (top plot) and forcounterclockwise rotation (bottom plot) of the cam 40. In clockwiserotation (top plot), the contact portion 20 contacts feature F2 followedquickly by encountering feature F1, followed by a long interval and thenrepeating. That is, in the clockwise direction the pattern is “ . . .F2F1---F2F1---F2F1 . . . ”. On the other hand, in the counterclockwisedirection (bottom plot) the contact portion 20 contacts feature F1followed quickly by encountering feature F2, followed by a long intervaland then repeating. That is, in the counterclockwise direction thepattern is “ . . . F1F2---F1F2---F1F2 . . . ”. While FIG. 2 shows twoasymmetrically positioned bumps F1, F2 of different heights, moregenerally the direction detection employs an asymmetric set of one ormore features that produce either (1) a signal feature for rotation inone direction or (2) a distinguishable time-reversed signal feature forrotation in the opposite direction. The set of features could be as fewas a single feature, e.g. a bump having a sharp slope on one side and ashallow slope on the other side to produce an asymmetric pulse in thevoltage versus time signal.

With returning reference to FIG. 1, the rotational directiondetermination approach described with reference to FIGS. 2 and 3 issuitably implemented by a pulse shape analyzer 90 that analyzes theshape of pulses (or pulse groups) in the voltage-versus-time signal, anddetermines a rotational direction 92 based on the pulse shape, where itis understood that the pulse shape for rotation in one direction will bethe time-reversed version of the pulse shape for rotation in theopposite direction. The pulse shape analyzer 90 suitably normalizes theelectrical frequency (or the spacing between pulses) to normalize forrotation speed.

With reference to FIGS. 4 and 5, side sectional and perspective views ofone embodiment of the sensor 10 of FIG. 1 are shown. The illustrativesensor 10 includes the aforementioned electrically conductive coil 12sealed in the housing 14 with sealed outer volume 22 and unsealed innervolume or cavity 24, the movable element, i.e. cam follower 16 includingthe permanent magnet 18, contact portion 20, and stop 32 engaging thewall 26, and the spring 30. The magnet 18 is magnetically held to thebody of the cam follower 16, which as seen in FIG. 4 also has a “cup” orrecess formed into it to help hold the magnet 18. In the embodiment ofFIGS. 4 and 5, there is no seal between the opening in the wall 26 andthe protruding contact portion 20 of the cam follower 16, but the fit isrelatively tight so that water flow might be constricted through the gapbetween wall 26 and contact portion 20. Such constriction in the waterflow could be detrimental since water pressure inside the cavity 24could create hydraulic impedance to movement of the cam follower 16.Accordingly, in the embodiment of FIGS. 4 and 5 the wall 26 includesflow holes 100 to provide enhanced fluid communication between theunsealed cavity 24 and the outside ambient (e.g. water). Theillustrative sensor 10 of FIGS. 4 and 5 also includes a ball bearing 102at the tip of the contact portion 20. Such a ball bearing, whileoptional, can facilitate unimpeded movement of the cam surface 42 acrossthe contact portion 20. Other smoothing approaches can be employed, suchas having the tip of the contact portion 20 be a single piece (i.e., noball bearing) but rounded to reduce friction, and/or applying alubricating solid coating to the tip, or so forth. As seen in FIG. 4,the MI cable 52 is welded to the housing 14 at an annular weld 104, andfurther welds 106 (shown in FIG. 5) secure the wall 26 to the main bodyof the housing 14, so as to ensure sealing of the outer volume 22containing the electrically conductive coil 12. It will be appreciatedthat the sensor 10 of FIGS. 4 and 5 is a single component that isreadily installed in any high temperature and/or high pressureenvironment.

The strength of the electrical signal (e.g. voltage) induced in theelectrically conductive coil 12 during operation of the sensor 10depends upon numerous factors. The magnetization of the magnet 18 is oneapparent factor, which can be improved by using a highly magnetizablematerial such as SmCo. Another factor is the number of turns (N) of thecoil 12, as the induced voltage is (at least approximately) proportionalto N. In the sensor of FIGS. 4 and 5, the electrically conductive coil12 includes several layers of turns. The overall geometry also impactsthe electrical signal. If the magnet is placed in the middle of a longcoil, then the change in magnetic flux through the coil may not changesignificantly as the magnet moves. In the embodiment of FIGS. 4 and 5,the magnet 18 is placed so that it is at one end of the encircling coil12 when the cam follower 16 is in its rest position (i.e., with the stop32 pressed against the wall 26 by the compressed spring 30). In thisgeometry, when the contact portion 20 is pushed to move the cam follower16 (further) into the cavity 24, this causes the magnet 18 at the end ofthe coil 12 to be pushed into the coil 12, which geometry should providea larger change in magnetic flux through the coil 12.

Another factor impacting the strength of the electrical signal (e.g.voltage) induced in the electrically conductive coil 12 during operationof the sensor 10 is the contouring of the cam surface 42. As perMaxwell's equations, the voltage induced in a coil is dependent on therate of change of the magnetic flux through the coil, rather than beingdependent on the magnitude of the magnetic flux through the coil. As aconsequence, rapid relief changes in the cam surface 42 are expected toprovide a larger signal than gradual relief changes. This motivatestoward, for example, having the rotary cam 40 with its cam surface 42being a side surface of the rotary cam 40 having a constant radiusexcept for one (or more) sharp bumps or depressions. Each bump ordepression produces a large-amplitude pulse in the coil. In the samevein, the rate of change in magnet position (or, equivalently, thereciprocation rate) also depends on the rotation speed of the rotary cam40, with the signal being expected to increase with increasing rotationspeed (this assumes the cam does not rotate so fast that the camfollower cannot follow the contouring of the cam surface). It isexpected that for a sensor 10 having the configuration shown in FIGS. 4and 5, and employing a 0.5-inch SmCo magnet, voltages of order 150-200millivolts can be induced in the coil at a cam rotation speed of 75 rpm.

With reference to FIGS. 6-13, some illustrative embodiments of the cam40 are described.

FIGS. 6 and 7 show perspective and end views, respectively, of a cam 40a comprising a lock sleeve with a cam surface 42 a that is a sidesurface of the sleeve with slots S1 a, S2 a of machined into the sleeveto serve as features for causing reciprocation of the cam follower 16.The slots S1 a, S2 a are of different depths and are arrangedasymmetrically around the circumference of the cam surface 42 a,specifically at a 90° smallest angular separation in the illustrativeexample, so that rotational direction determination can be performed asalready described with reference to FIGS. 2 and 3. The sleeve 40 a maybe disposed over a rotor of a nut or other rotating element. Theillustrative sleeve 40 a is a locking sleeve that includes lockingfeatures 120 (visible only in FIG. 6).

FIGS. 8 and 9 show perspective and end views, respectively, of a cam 40b comprising a lock sleeve with a cam surface 42 b including a ring 122b formed by wire electrical discharge machining (EDM) or anothertechnique and tack welded or otherwise attached to the sleeve. The ring122 b is a side surface of the sleeve 40 b and includes bumps S1 b, S2 bof machined into the sleeve to serve as features for causingreciprocation of the cam follower 16. The bumps S1 b, S2 b are ofdifferent heights and are arranged asymmetrically around thecircumference of the cam surface 42 b, specifically at a 90° smallestangular separation in the illustrative example, so that rotationaldirection determination can be performed as already described withreference to FIGS. 2 and 3. The sleeve 40 b also includes the lockingfeatures 120 (visible only in FIG. 8).

FIGS. 10 and 11 show perspective and end views, respectively, of a locksleeve 40 c with a side surface 42 c including a ring formed by wireelectrical discharge machining (EDM) or another technique and tackwelded or otherwise attached to the sleeve. The ring includes slotsfilled with inserts S1 c, S2 c made of a magnetic material. In thisapproach, the cam follower 16 is replaced by a sensor arm made of amagnetic material that is magnetically coupled with the electricallyconductive coil 12, and one or both of (i) the sensor arm and (ii) theinserts S1 c, S2 c are magnetized. The sensor arm need not be movable,because movement is not what causes the time-varying magnetic fluxthrough the coil 12 in this embodiment. Rather, in this embodiment themagnetic flux flows through the coil when the magnetized inserts S1 c,S2 c move proximate to the sensor arm. Alternatively, if the sensor armis magnetized and the inserts are not, then the magnetic flux is reducedwhen the (non-magnetized) inserts S1 c, S2 c move proximate to the(magnetized) sensor arm. In some embodiments, the side surface 42 chaving the one or more inserts S1 c, S2 c has a constant radius (as seenin FIGS. 10 and 11) so that the contact between the sensor arm and theside surface 42 c remains uniform throughout each revolution. Theinserts S1 c, S2 c may be of different sizes (as shown) or be made ofdifferent materials, and are arranged asymmetrically around thecircumference of the side surface 42 c, specifically at a 90° smallestangular separation in the illustrative example, so that rotationaldirection determination can be performed as already described withreference to FIGS. 2 and 3. The sleeve 40 c also includes the lockingfeatures 120 (visible only in FIG. 10).

FIGS. 12 and 13 show perspective and end views, respectively, of a cam40 d comprising a lock sleeve with a cam surface 42 d including a ringformed by wire electrical discharge machining (EDM) or another techniqueand tack welded or otherwise attached to the sleeve. The ring is a sidesurface of the sleeve 40 d and includes bumps S1 d, S2 d of machinedinto the sleeve to serve as features for causing reciprocation of thecam follower 16. The bumps S1 d, S2 d are of different heights andlengths, and are arranged asymmetrically around the circumference of thecam surface 42 d, specifically at a 90° smallest angular separation inthe illustrative example, so that rotational direction determination canbe performed as already described with reference to FIGS. 2 and 3. Thesleeve 40 d also includes the locking features.

With reference to FIG. 14, an illustrative nuclear reactor 200 is shown,of the pressurized water reactor (PWR) variety. The illustrative PWR 200includes a nuclear reactor core 202 disposed in a pressure vessel 204.The reactor core 202 comprises a fissile material (e.g., ²³⁵U) immersedin primary coolant water. A cylindrical central riser 206 is disposedcoaxially inside the cylindrical pressure vessel 204 and a downcomerannulus is defined between the central riser 206 and the pressure vessel204. The illustrative PWR 200 includes internal control rod drivemechanisms (internal CRDMs) 208 with CRDM motors 210 that controlinsertion of control rods to control reactivity. Guide frame supports212 guide the translating control rod assembly (not shown; typicallyeach control rod assembly includes a set of control rods comprisingneutron absorbing material yoked together by a spider and connected viaa connecting rod with the CRDM). The illustrative PWR 200 is an integralPWR that includes an internal (or “integral”) steam generator 214located inside the pressure vessel, and more specifically in thedowncomer annulus defined between the pressure vessel 204 and thecentral riser 206. Embodiments in which the steam generator is locatedoutside the pressure vessel (i.e., a PWR with external steam generators)are also contemplated. The steam generator 214 is fed by a feedwaterinlet 216 and deliver steam to a steam outlet 218. The illustrative PWR200 includes an integral pressurizer 220 at the top of the pressurevessel 204 which defines an integral pressurizer volume; however anexternal pressurizer connected with the pressure vessel via suitablepiping is also contemplated. Primary coolant water in the pressurevessel 204 is circulated by reactor coolant pumps (RCPs) comprising inthe illustrative example external RCP motors 222 each driving animpeller located in a RCP casing 224 disposed inside the pressure vessel204. It is to be appreciated that the PWR 200 is merely an illustrativeexample—the disclosed operating procedures are suitably employed insubstantially any type of PWR.

With continuing reference to FIG. 14, for performing measurements of theCRDM motion during reactor operation, the sensor 10 is suitably disposedinside the pressure vessel 204, for example positioned for the contactportion of the cam follower to cam against a nut of the CRDM motor 210.While a single sensor 10 is diagrammatically shown in FIG. 14, it is tobe appreciated that each CRDM motor may include such a sensor. If thetotal number of CRDMs is N_(CRDM), then this requires N_(CRDM) sensors,and 2×N_(CRDM) electrical wires (all signal wires; none carry power). Itis to be further appreciated that the illustrative sensor 10 is shownoversize in FIG. 10 in order to be visible in the diagrammaticrepresentation.

With reference to FIG. 15, two illustrative operational positions of thesensor 10 for monitoring movement in a CRDM are shown. The illustrativeCRDM employs a nut-and-screw mechanism in which a rotary nut 300 drivenby a motor (not shown; however, in some embodiments the nut 300 may bepart of the motor rotor). The nut 300 is prevented from translating upor down by a suitable fixture (not shown), and rather a screw 302engaged by the nut 300 translates up or down as the nut 300 rotates. Thenut 300 serves as the cam 40 of FIG. 1, and its side surface serves asthe cam surface 42 that is engaged by a sensor 10 _(Nut) which issuitably the sensor 10 of FIGS. 4 and 5, for example. The side surfaceof the nut 300 (or a lock ring or lock sleeve attached thereto, e.g. asin the examples of FIGS. 8-13) suitably includes one or more features304, e.g. two features 304 of different types that correspond to thefeatures F1, F2 of FIG. 2 and enable both nut rotation speed (ordistance) and nut rotation direction to be determined. The nut rotationspeed or distance can be converted to linear translation distance of thescrew 302 based on the thread pitch. (Note that if the pitch of thethreads are known, then determination of rotation direction alsodetermines whether the screw translation is upward or downward).

As also shown in FIG. 15, in an alternative approach a sensor 10_(Screw) (which again may be the sensor 10 of FIGS. 4 and 5, forexample) engages the screw 302 directly. In this case the screw 302serves as the cam which the contact portion 20 of the cam follower ofthe sensor 10 _(screw) contacts. As the screw 302 moves upward ordownward responsive to rotation of the nut 300. Each passage of onethread of the screw 302 produces a pulse (or other feature in thevoltage-versus-time signal) and the corresponding distance is the threadpitch. This approach does not readily provide direction information;however, the angle of the pitch may provide enough difference in thesignal feature for up-versus-down motion to ascertain the direction oftranslation of the screw 302. It is to be appreciated that this approachis also suitably applied to some other CRDM mechanisms. For example, ina rack-and-pinion mechanism the rack is analogous to the screw, and thesame approach can be applied except that the sensor in the case of arack-and-pinion mechanism senses passage of gear teeth of the rack, andthe translation distance is computed based on the spacing of the gearteeth on the rack.

The approach of either sensor 10 _(Nut) or sensor 10 _(Screw) may beapplied to an operational CRDM (e.g., as diagrammatically shown in FIG.14), or can be applied to a test apparatus in which the CRDM is in atest pressure vessel.

While disclosed in the context of a nuclear reactor and for the task ofsensing CRDM motion, the disclosed sensors and sensing approaches areapplicable to other motion measurement tasks that may need to beperformed in a high pressure environment (e.g., a pressure of at least725 psia, and more particularly a pressure of at least 1450 psia in thecase of a typical nuclear reactor) and/or a high temperature environment(e.g., at least 212° F. corresponding to boiling water at atmosphericpressure, and more particularly a temperature of at least 450° F. in thecase of a nuclear reactor). It is contemplated to employ the disclosedsensing approaches at elevated pressure but room temperature, or atatmospheric pressure and elevated temperature, or at both elevatedpressure and elevated temperature (as in the case of a nuclear reactor).

The preferred embodiments have been illustrated and described.Obviously, modifications and alterations will occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

We claim:
 1. An apparatus comprising: a rotary cam including a sidesurface, and a sensor including: an electrically conductive coil, ahousing having an unsealed inner volume, the electrically conductivecoil being sealed inside the housing and encircling the unsealed innervolume, a cam follower including (i) a permanent magnet that is disposedin the unsealed inner volume and is magnetically coupled with theelectrically conductive coil and (ii) a contact portion extendingoutside the housing, the cam follower being movable respective to thehousing such that force applied to the contact portion moves thepermanent magnet respective to the electrically conductive coil togenerate an electrical signal in the electrically conductive coil; and aspring disposed inside the unsealed volume that biases the cam followertoward a rest position such that force applied to the contact portionmoves the engagement element away from the rest position against thespring and the spring returns the engagement element to the restposition upon removal of the force, wherein the cam follower engages theside surface of the rotary cam, the side surface being shaped to producereciprocation of the cam follower when the rotary cam rotates.
 2. Theapparatus of claim 1 wherein the unsealed inner volume is defined inpart by a wall having an opening out of which the contact portion of themovable element extends, and the spring biases a stop of the movableelement against the wall.
 3. The apparatus of claim 2 wherein a gapbetween the movable element and the constricted opening of the wall isan unsealed gap.
 4. The apparatus of claim 2 wherein the wall includesflow holes.
 5. The apparatus of claim 1 wherein the cam followerincludes a ferromagnetic main body and the permanent magnet is separatefrom the ferromagnetic main body and is magnetically connected to theferromagnetic main body.
 6. An apparatus comprising: a rotary camincluding a side surface, and a sensor including: an electricallyconductive coil, a housing having an unsealed inner volume, theelectrically conductive coil being sealed inside the housing andencircling the unsealed inner volume, and a cam follower including (i) apermanent magnet that is disposed in the unsealed inner volume and ismagnetically coupled with the electrically conductive coil and (ii) acontact portion extending outside the housing, the movable element beingmovable respective to the housing such that force applied to the contactportion moves the permanent magnet respective to the electricallyconductive coil to generate an electrical signal in the electricallyconductive coil, wherein the cam follower engages the side surface ofthe rotary cam, the side surface being shaped to produce reciprocationof the cam follower when the rotary cam rotates.
 7. The apparatus ofclaim 6 further comprising: a readout device connected to measure theelectrical signal generated in the electrically conductive coil; and anelectronic data processing device configured to compute a rotation rateor rotation distance of the rotary cam based on the measured electricalsignal.
 8. The apparatus of claim 7 wherein the rotary cam has aconstant-radius side surface with N surface features producing N pulsesin the measured electrical signal for each revolution of the cam, whereN is greater than or equal to one, and the electronic data processingdevice is configured to compute a rotation rate of the rotary cam asequal to the pulse frequency divided by N.
 9. The apparatus of claim 7wherein the rotary cam has a constant-radius side surface with anasymmetric set of one or more features that produce a signal feature ora distinguishable time-reversed signal feature in the measuredelectrical signal depending upon rotation direction of the rotary cam,and the electronic data processing device is further configured todetermine rotation direction of the rotary cam based on detection of thesignal feature or the time-reversed signal feature in the measuredelectrical signal.
 10. The apparatus of claim 7 wherein the rotary camis a nut of a control rod drive mechanism (CRDM) that engages a screw ofthe CRDM, and the electronic data processing device is furtherconfigured to compute a linear translation rate or linear translationdistance of the screw based on the computed rotation rate or rotationdistance and a thread pitch of the screw.
 11. The apparatus of claim 10wherein the rotary nut and the sensor are both disposed in water at atemperature of at least 212° F., and the unsealed inner volume of thehousing of the sensor is filled with the water.
 12. The apparatus ofclaim 11 wherein the sensor and the CRDM including the rotary nut areboth is disposed in a nuclear reactor and are both immersed in primarycoolant water of the nuclear reactor at a temperature of at least 450°F. and a pressure of at least 1450 psia, and the unsealed inner volumeof the housing of the sensor is filled with primary coolant water. 13.An apparatus comprising: a control rod drive mechanism (CRDM) includinga screw or a rack, a sensor including: an electrically conductive coil,a housing having an unsealed inner volume, the electrically conductivecoil being sealed inside the housing and encircling the unsealed innervolume, and a cam follower including (i) a permanent magnet that isdisposed in the unsealed inner volume and is magnetically coupled withthe electrically conductive coil and (ii) a contact portion extendingoutside the housing, the movable element being movable respective to thehousing such that force applied to the contact portion moves thepermanent magnet respective to the electrically conductive coil togenerate an electrical signal in the electrically conductive coil,wherein the cam follower engages the screw or rack such that threads ofthe screw or gear teeth of the rack produce reciprocation of the camfollower as the cam moves linearly.
 14. The apparatus of claim 1 whereinthe sensor is a passive sensor that does not receive electrical powerand has only two electrical leads.